Refineries for processing of crude oils (or crude oil fractions) currently face a variety of challenges. For example, crude refining is the most energy intensive industry in the United States. As a result, refineries have implemented energy conservation programs, as well as energy integration and efficiency projects. However, even though these programs have resulted in lower energy consumption, the reality is that most existing refineries were built between the 1950s and 1970s, when energy was cheap and the products could be directly sent to market without the need for further processing.
Refineries also face pressure due to the increasing requirements on the specifications for various products. These product specifications may be driven by either government regulation or by the demands of the marketplace. The standard response from the industry to date has largely consisted of adding carbon rejection and/or hydrogen addition steps downstream of existing processes. This has placed further strain on the hydrogen needs of existing refineries. This also tends to exacerbate the problems of energy usage, as large process energy consumers have been introduced that are needed to meet product quality specifications.
The above problems have also contributed to increasing profitability concerns for refineries. Due in part to the price of crude oil, the expense of complying with additional product specifications, and changes in marketplace demand, it is increasingly important for a refinery to improve or maximize the number of carbon atoms that are incorporated into higher value products. Pending CO2 legislation would further increase refining costs, if enacted. Based on the variety of challenges facing refineries, improved methods of refining crude oils are desirable.
U.S. Pat. No. 3,617,501 describes an integrated process for refining a whole crude. The entire crude (including naphtha) is initially hydrotreated, followed by separation in an atmospheric distillation tower. The naphtha and distillate portions are used for fuels. The heavier portions are either separated using a vacuum distillation tower or are sent to a hydrocracker for extinction recycle.
U.S. Pat. No. 5,851,381 describes methods of refining crude oil. The various methods include flashing a crude oil to initially separate out a naphtha and lighter portion from the remainder of the crude oil. The remaining portion of the crude is then hydrodesulfurized and/or hydrotreated. At some point, the remaining portion is separated by what is described as an atmospheric distillation tower. However, this tower is also described as generating a heavy gas oil fraction with a boiling range of 371° C. to 472° C. Separation of such a heavy gas oil fraction in a conventional atmospheric distillation tower would be expected to result in substantial coke formation. As a result, generating such a fraction is normally indicative of the use of a vacuum distillation technique.
U.S. Published Patent Application US 2010/0025291 describes a process for treatment of heavy oils using light hydrocarbon components as a diluent. Hydrotreatment is performed on a heavy crude by processing the whole crude, including the naphtha and distillate fractions. A portion of the naphtha and/or distillate after hydrotreatment is also recycled to achieve a desired relative amount of lighter hydrocarbons to heavy oil. The catalyst for hydrotreatment is described as a supported NiMo catalyst, but no description is provided regarding the pore sizes of the support. The atmospheric residue portion of the whole crude is desulfurized to a level of about 5000 wppm in one example.
U.S. Published Patent Application US 2010/0025293 describes a process for sequential hydroconversion and hydrodesulfurizaton of whole crude oil. A bimodal catalyst with one mode of pore sizes greater than at least 2000 angstroms is used for the hydroconversion. The reactors for hydroconversion and hydrodesulfurization are described as preferably being ebullating bed reactors.